Draft regulator



March 26,1940; J. w. MILLER 2,194,608

DRAFT REGULATOR Filed Jan. 3, 193a k k E Q 3% #761 4 E INVENTOR. 1 JOHN W M/LLEE BY z= smc-z DflFT 6M4. il/L F/g; 3' ATTORNEY.

Patented Mar. 26, 1

UNITED STATES DRAFT REGULATOR John w. Miller, Lansing, Mich, assignor to Motor Wheel Corporation, Lansing, Mich, a corporation of Michigan Application January 3, 1938, Serial No. 182,993

3 Claims. (01. 230-45) This invention relates to draft regulators for combustion apparatus, and more particularly to draft regulators of the type which are adjustable to vary the draft in the combustion apparatus.

This invention is an improvement on the regulator disclosed in the application of Don F. Jones, Serial No. 132,675, filed March 24, 1937.

Although this invention is adapted for use in any type of combustion apparatus, it is par- 16 ticularly suitable to oil burners of the so-called vaporizing pot type. Oil burners of the vaporizing pot type areparticularly sensitive to changes in draft, and consequently it is desirable to provide a draft regulator that will hold the draft id in the burner substantially constant within a reasonably wide range of stack drafts.

It is accordingly an object of this invention to provide a draft regulator that will be adjustable I to vary the draft in the burner but will keep such draft substantially constant when once set at the desired position.

' Another object of the invention 'is to provide formulae by means of which the important dimensions of any size of regulator can be readily as calculated. In the drawing: I Figure l is an elevational view of the improved draft regulator; 4

2 is a sectional view taken on substang-e tially the line 2-2 of Figure'l;

Figure 3 is a copy of a curve sheet showing the results of a series of tests under actual working conditions of the regulator disclosed herein in' comparison with a regulator of a previous type; so and Figure 4 is a diagram of a regulator blade showing the location of the pivot axis.

Referring now more particularly to the draw ing, the numeral HI designates a pipe which is adapted to be connectedto a flue outlet or a stack of an oil burner of any conventional type, not shown. Telescopically inserted in the outer end of the pipe It is an annular ring ii of angular cross-section which is adapted to receive the 5 blade E2 of the regulator.

The blade 52 is'preferably stamped from a. single sheet of metal, and is provided with annular ribs ii and I4 which tend to stiffen the blade as well as improve its appearance. The

50 blade i2 is slit at a plurality of points it and the metal on opposite sides of the slits is pressedin opposite directions in order to provide a support for a pivot shaft H. The metal of the ring II is also slit and deformed at it to receive the ends of the pivot shaft H. In this manner the following formula:

P. F: A

where P. F. is the power factor, A is the area. of the lower segment of the blade, A" is the area of the upper segment, and A is the total area of the blade.

It has been determined experimentally that for best results the. power factor of the regulator should be approximately Stated differently, the ratio of the area of the lower segment to the area of-the upper segment should be about 1.875. To produce such a power factor the pivot axis should lie on a chord of the circle subtending 152 of arc. In Figure 4 the chord is designated by the letter C and the angle subtended thereby is designated by the letter E. The center line of the circle is indicated by the letters CL. F designates an angle which is one-half of the difference between the angle E and 180, or in this case 14. 30

The perpendicular'distance of the chord C from the center line CL of the blade may be determined by the following formula:

where R-H is the distance desired, R is the radius of the blade and F is the angle shown in Figure. 4. Assuming that it is desired to calculate the distance R-H for a blade of 8%" diameter,

which would be the proper size for a 9" pipe: RH;4% sine 14 X .2419 =.998,

or for all practical purposes, 1 inch.

Near th upper portion of the blade l2 an oilfset i5 is pressed therein; The center of the circular offset 15 has an opening therein in which is rigidly secured a sleeve 2|. The inner surface of the sleeve 2| is threaded for the reception of an externally threaded shaft 22 to which a weight 23 is rigidly attached. As shown, the weight 23 is threaded onto a reduced portion 24 of the shaft 22 and theend of the shaft is peened over as at 25 to permanently attach the weight 23 to the shaft.

The threads on the shaft 22 are of a high lead whereby when the shaft 22 is rotated it will adjust the weight toward or away from the plane I of the blade I2 and will give a sufficient range of adjustment within one complete revolution of the shaft. The offset I5 is of such a depth that when the weight 23 is adjusted so as to be as close as possible to the bottom of the offset I5 the entire blade and its weight 23 will be statically balanced in both its horizontal and vertical positions. Then when the shaft 22 is rotated through one revolution from its low to its high position the weight will be spaced from the blade a sufficient distance to give the requisite high draft that is desired at certain times.

The axis of the shaft 22 theoretically could lie anywhere on a vertical diameter of the blade and the device could still be statically balanced by the use of a proper weight. However, in order that the device will operate at maximum efliciency, it has been found that the location of the axis of the shaft 22 is approximately it of an inch from the pivot axis I1. If the axis of the shaft 22 is moved further away from the pivot shaft I! the action of the damper is changed so that the burner draft does not remain constant at the higher stack drafts but instead tends to decrease,

so that the curves of Figure 3 break over and fall off. On the other hand if the weight is moved too near to the axis I! the action of the damper is changed so that the curves shown in Figure 3 climb gradually and do not level off.

The weight necessary to balance the various sizes of regulators will vary and can best be determined by experiment. However, as a practical matter, the thickness of all of the weights should be the same in order that the depth of the depression or offset I5 can be kept the same for each side of the blade. The mass of the weight 23 can be varied by changing its diameter. It has been found that a depth of offset of 01' an inch is suitable, although this dimension is not critical. The thickness of the weight is dependent on the depth of the offset.

The weight 23 is of substantially frusto-conical shape so that the center of gravity thereof is not at the center of the weight but is offset slightly toward the plane of the blade. The weight 23 is provided with a substantially circular recess 26 into which is inserted a packing of felt 21 or the like which is preferably fixed to the interior surface of the recess 26 by a cement that will not char or harden. v The felt 21 fits snugly against the exterior surface of the sleeve 2.I to prevent corrosion of the surface of said sleeve and the deposit of soot thereon.

The end of the shaft 22 opposite the weight has a pointer 28 and a knob 29 attached thereto in the same manner as the weight,23. The knob provides for rotation of the shaft 22 and the pointer indicates the relative position of the weight.

A stop 30 is attached to the ring I I adjacent one end of the pivot shaft IT. A lower portion'3I of the stop is substantially in the plane of the blade when it hangs in its vertical position and is located on the exterior surface of the ring II so that the major segment I 9 of the blade I 2 cannot swing outwardly. The upper end 32 of the stop 3|! extends out from the plane of the ring and is so adjusted that the major segment I9 of the blade cannot swing too far inward.

An auxiliary weight 33 is attached by a screw 34 adjacent the lower edge of the major segment I9 of the blade I2. This weight is readily removable, as in some cases its use is unnecessary.

The auxiliary weight 33 is necessary only when the pipe I0 is attached to a vertical flue outlet or stack extending from the combustion chamber. Ordinarily the draft regulator is mounted so close to the usual flue outlet or stack that when the blade I2 rotates any substantial amount from its vertical position the lower portion IQ of the blade I2-will extend into the path of the rapidly moving hot gases emanating from the combustion chamber. If the draft regulator is mounted on a vertical stack as aforementioned, when the blade I2 swings into the path of the gases they will impinge on the lower portion of the blade and will tend to upset the required balance of the regulator as a whole. Consequently, the weight 33 is used to offset the force of the rapidly moving gases when the regulator is mounted in a vertical stack.

If the regulator is mounted on a horizontal flue outlet, however, the plane of the blade l2 will lie in the path of the gases escaping from the combustion chamber when it is swung to its inward position, and consequently, the gases will have no effect on the position of the blade. In such a case the weight 33 is dispensed with.

When the burner is in operation, the hot gases escaping up the stack create a draft in the bumer that supplies air for combustion. The draft thus created fluctuates widely due to changes in atmospheric pressure and temperature, and also to variations in wind velocity and direction. The automatic draft regulator above'described swings on its pivot as the draft within the stack changes and allows more or less air to enter through the pipe III, thereby keeping the burner draft substantially constant.

By rotating the threaded shaft 22 the weight 23 may be moved toward or away from the blade, thus changing the air pressure required to swing the blade I2 about its pivot. Once the weight has been adjusted to give a certain burner draft, measured in inches of water, the regulator will hold that draft substantially constant, despite variations in the stack draft. and the burner will operate at its maximum efllciency.

The curve sheet shown in Figure 3 of the drawing indicates the marked difference produced by this invention over draft regulators of previous designs. This difference is primarily due to the formation of the offset I5 so that the weight 23 can be adjusted to a point where the center of gravity of the weight and shaft lie substantially in the plane of the blade I2. The three curves .shown in full lines in Figure 3 show results of tests on the regulator of this invention, whereas the three curves shown in dotted lines represent the operation of a regulator identical with the one herein shown except that there is no ofiset IS. The curve A shows the practically constant burner draft at the low setting oi. the indicator 23, whereas curve A shows the corresponding setting on the older type of regulator. B and B show the corresponding drafts at the medium setting of both devices, and C and C show the drafts created at the high setting of both types of regulators.

The abscissae of the curves of Figure 3 are the stack drafts and the ordinates are the drafts in the burner, both measured in inches of water. The stack drafts range from 0 to .2 inch or possibly even higher under certain conditions. The burner draft at low setting (curve A) is about .02

inch and, as will be seen, does not vary over approximately .01 of an inch after the blade begins to open. It requires a stack draft of .04 .inch or more to produce'a burner draft of .02 inch. The

medium setting of the weight (curve B) gives a burner draft of between .04 and .05 inch with stack drafts of .07 inch and up, and the high setting (curve C) gives a burner draft of about .08 inch with stack drafts of .11 andup.

, If the blade l2 could be fitted tightly into the ring ll, there would be no leakage of air past the blade when the latter is in its closed position. Therefore, the curves would all lie on a straight line at an angle of. 45 degrees to both the X and Y, or stack draft and burner draft axes from zero draft to the points where the blade begins to open. In other words, the stack drafts, and burner drafts would be equal up to the points where the blade begins to swing on its pivot At these points the various curves would break away from the straight line.

Because there is always a certain amount of leakage, however, the curves are not on one straight line at low drafts, and the inclination of the curves is not 45 degrees. The leakage accounts for the difference between the curves at low drafts.

The curves A, B and C rise higher than curves A, B and C and do not level off because the weight is spaced farther from the blade at each setting than it is at the corresponding setting on the bladeof this invention. Consequently a higher stack draft is required to move the blade of the previous type than is necessary in the device disclosed herein.

Comparing the results obtained with the two regulators it will be apparent that with the former type the burner draft rises continually as the stack draft increases, and does not level ofi and become constant when the proper operating stack draft is reached. With the regulator described herein, however, the burner draft remains practically constant despite fluctuations in the stack drait.

Not only does the invention disclosed herein hold the draft in the burner substantially constant within the usual operating range of stack drafts, but it also makes possible the proper con-.

trol of thelower burner drafts, such as drafts of .02 inch of water.

It will be readily apparent that the invention herein disclosed is a marked improvement over prior adjustable draft regulators, and I desire the invention to be limited only by the scope of the appended claims.

Iclaim:

1. A draft regulator for combustion apparatus comprising a frame member having an opening therein, a circular blade oi. a size to substantially completely fill said opening, said blade being pivoted on said frame member on an axis in the plane of the blade and coincident with a chord of said circular blade subtending 152 degrees of arc, thereby dividing said blade into a mjor segment and a minor segment, an offset in the minor segment of the blade and a weight mounted in the offset for adjustment normal to said blade, said weight being of such size that the blade is statically balanced in both its vertical and horizontal positions when the weight is in the position closest to the blade.

2. A draft regulator for combustion apparatus comprising, in combination, a frame member having an opening therein, a blade of a size to substantially completely fill said opening, said blade being mounted in said frame member on a pivot located above the center thereof thereby dividing said blade into a major segment and a minor segment, an ofl'set in the minor portion of said blade forming a recess therein, a weight adiustably mounted for movement perpendicular to said blade and into and out of said recess and movable to a position wherein the center of gravity of said weight is substantially in the plane oi the blade, said weight being of such size that its weight plus the weight of the minor portion of the blade equals the weight of the major portion of. the blade, and said weight being so located with respect to the 'pivot axis of the blade that when the weight is as close as possible to said blade the turning movement of the two sides of the blade are substantially balanced.

3. A draft regulator for combustion apparatus comprising a frame member having an opening therein, a circular blade of a size to substantially fill said opening, said blade being pivoted on said frame member on an axis in the plane of the blade and coincident with a chord of said blade located at one side of the center thereof thereby dividing said blade into a'major segment and a minor segment, an offset forming a recess in the minor segment of the blade, and a weight mounted in the offset for adjustment normal to said blade, said weight being of such size that its welghtplus the weight of the minor portion of the blade equals the weight of the major portion oi-the blade and said weight being so located with respect to the pivot axis of the blade that when the weight is as close as possible to said blade the turning moments of the two sides of the blade are substantially balanced.

JOE W. MINER.

I CERTIFICATE OF CORRECTION. Patent No. 2 l91 l, 608. March 26, 191 .0.

' JOHN w.' MILLER.

is hereby certified that error appears in the printed specification of the abeve numbered patent requiring correction as follows: Page 5, sec

ond' column, line 55, claim'2, for the word "movement" read -moment-; an

that the said Letters Patent should be read with this correction therein that the same may conform to the record of the case in the Patent Office.

Signed and sealed this 7th day of May, A. D. 191p.

. Henry Van Arsdale, (Seal) Acting Commissioner of Patents. 

